As wireless communication systems such as cellular telephone, satellite, and microwave communication systems become widely deployed and continue to attract a growing number of users, there is a pressing need to accommodate a large and variable number of communication subsystems transmitting a growing volume of data with a fixed resource such as a fixed channel bandwidth accommodating a fixed data packet size. Traditional communication system designs employing a fixed resource (e.g., a fixed data rate for each user) have become challenged to provide high, but flexible, data transmission rates in view of the rapidly growing customer base.
The third generation partnership project long term evolution (“3GPP LTE”) is the name generally used to describe an ongoing effort across the industry to improve the universal mobile telecommunications system (“UMTS”) for mobile communications. The improvements are being made to cope with continuing new requirements and the growing base of users. Goals of this broadly based project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards and backwards compatibility with some existing infrastructure that is compliant with earlier standards. The project envisions a packet switched communications environment with support for such services as VoIP (“Voice over Internet Protocol”) and Multimedia Broadcast/Multicast Services (“MBMS”). MBMS may support services where base stations transmit to multiple user equipment simultaneously such as mobile television or radio broadcasts, for example. The 3GPP LTE project is not itself a standard-generating effort, but will result in new recommendations for standards for the UMTS.
The UTRAN includes multiple Radio Network Subsystems (RNSs), each of which contains at least one Radio Network Controller (RNC). However, it should be noted that the RNC may not be present in the actual implemented systems incorporating Long Term Evolution (LTE) of UTRAN (E-UTRAN). LTE may include a centralized or decentralized entity for control information. In UTRAN operation, each RNC may be connected to multiple Node Bs which are the UMTS counterparts to Global System for Mobile Communications (GSM) base stations. In E-UTRAN systems, the e-Node B may be, or is, connected directly to the access gateway (“aGW,” sometimes referred to as the services gateway “sGW”). Each Node B may be in radio contact with multiple UEs (generally, user equipment including mobile transceivers or cellphones, although other devices such as fixed cellular phones, mobile web browsers, laptops, PDAs, MP3 players, gaming devices with transceivers may also be UEs) via the radio Uu interface.
The wireless communication systems as described herein are applicable to, for instance, 3GPP LTE compatible wireless communication systems and of interest is an aspect of LTE referred to as “evolved UMTS Terrestrial Radio Access Network,” or E-UTRAN. In general, E-UTRAN resources are assigned more or less temporarily by the network to one or more UEs by use of allocation tables, or more generally by use of a downlink resource assignment channel or physical downlink control channel (PDCCH). LTE is a packet-based system and, therefore, there may not be a dedicated connection reserved for communication between a UE and the network. Users are generally scheduled on a shared channel every transmission time interval (TTI) by a Node B or an evolved Node B (e-Node B). A Node B or an e-Node B controls the communications between user equipment terminals in a cell served by the Node B or e-Node B. In general, one Node B or e-Node B serves each cell. A Node B may be referred to as a “base station.” Resources needed for data transfer are assigned either as one time assignments or in a persistent/semi-static way. The LTE, also referred to as 3.9G, generally supports a large number of users per cell with quasi-instantaneous access to radio resources in the active state. It is a design requirement that at least 200 users per cell should be supported in the active state for spectrum allocations up to 5 megahertz (MHz), and at least 400 users for a higher spectrum allocation.
In order to facilitate scheduling on the shared channel, the e-Node B transmits a resource allocation to a particular UE in a downlink-shared channel (PDCCH) to the UE. The allocation information may be related to both uplink and downlink channels. The allocation information may include information about which resource blocks in the frequency domain are allocated to the scheduled user(s), the modulation and coding schemes to use, what the size of the transport block is, and the like.
One service supported by E-UTRAN UEs and E-Node Bs is discontinuous reception (“DRX”). In discontinuous reception, the UE is arranged to conserve its power consumption (typically, the UE is battery powered and the battery life is a critical aspect of the convenience of the equipment). The UE enters (or may be instructed to enter by the e-Node B) a DRX sleep or standby period for a determined period and at the end of the period, the UE checks the DL channel to determine if resources are allocated to the UE in the present sub frame. If no resources are allocated the UE may again enter a DRX standby cycle. During standby cycles as much of the receiver and transmitter circuitry in the UE as possible is powered down to conserve battery power. The e-Node B is arranged to be aware of the operation of the UEs that are connected to it and is aware that they are performing DRX.
The lowest level of communication in the e-UTRAN system, Level 1, is implemented by the Physical Layer (“PHY”) in the UE and in the e-Node B and the PHY performs the physical transport of the packets between them over the air interface using radio frequency signals. In order to ensure a transmitted packet was received, an automatic retransmit request (“ARQ”) and a hybrid automatic retransmit request (“HARQ”) approach is provided. Thus whenever the UE receives packets through one of several downlink channels, including command channels and shared channels, the UE performs a communications error check on the received packets, typically a Cyclic Redundancy Check (CRC), and in a later sub frame following the reception of the packets, transmits a response on the uplink to the e-Node B or base station. The response is either an Acknowledge (ACK) or a Not Acknowledged (NACK) message. If the response is an NACK, the e-Node B automatically retransmits the packets in a later sub frame on the downlink or DL. In the same manner, any UL transmission from the UE to the e-Node B is responded to, at a specific sub frame later in time, by a NACK/ACK message on the DL channel to complete the HARQ. In this manner, the packet communications system remains robust with a low latency time and fast turnaround time.
The types of UEs the e-UTRAN environment can accommodate are many. One type of UE that is presently proposed to be supported in e-UTRAN systems is a half duplex FDD UE. This type of UE can only receive (be in downlink mode) or transmit (be in uplink mode) at a particular time but cannot be in both modes simultaneously, unlike a full duplex UE. The half duplex UEs proposed will also have DRX services. The need to accommodate a half duplex UE in the environment poses several problems for the system. A need thus exists for methods and apparatus to support half duplex UEs in the e-UTRAN environment. The addition of support for half duplex UEs must have a minimum impact on the efficiency and operation of the remaining services in the environment, the other UEs, the e-Node B devices, and mobile management entities (“MMEs”).